Eighth-grade student scientists enjoyed a series of fun lab experiments to learn more about the Laws of Conservation of Matter and Mass in class last week. This key law of science says that matter can be neither created nor destroyed, which means the total mass of the system remains constant during any physical or chemical change. In other words, even though you can watch matter change before your very eyes, the total mass will remain the same even as and after it undergoes transformation.
Students donned gloves and safety goggles before tackling their experiments in small teams.
First, they explored the question: Where did it come from? They poured a small amount of copper sulfate into a small beaker and placed an iron nail in the solution, leaving the top of the nail sticking out. The chemical reaction takes a bit of time, so our intrepid scientists moved on to the next step in their experiment:
Where did it go? Each team had a scale, a crucible, toothpicks, and matches. They placed the empty crucibles on their scales and zeroed them out. Then they added toothpicks and a match to their crucibles and noted how much they weighed, recording the weight of the combined wood on their worksheets. Then, one member of each team lit the match and dropped it into the crucible, burning both the match and the toothpicks. They watched the number on the scale as the wood burned, and recorded the final weight of the wood after it was finished burning. They pondered questions like what happened to the weight as the wood burned, where did it go (did you destroy matter), and what reactant was there besides wood? What products were made?
Students discovered that burning the wood made the mass decrease, but they deduced that the matter was not destroyed; it just changed into smoke, which floated off the scale. In fact, over 90% of the woods’ mass became smoke and escaped into the classroom air.
Their third experiment offered them a look inside an open system and a closed system. This project involved using Alka-Seltzer tablets. First, each team weighed an Alka-Seltzer tablet and recorded their finding. Then, they weighed a beaker with 100 mL of water and recorded that data. They predicted what the combined weight of the tablet and the beaker of water, before placing the beaker on the scale and dropping in the Alka-Seltzer tablet. As the beakers fizzed, they observed the reaction and recorded the actual combined weight of the tablet and beaker of water. This is an example of an open system.
The second part of this experiment involved breaking the tablet into a couple of pieces and placing them inside a balloon. They recorded the weight of the balloon and tablet, and, separately, the weight of a flask with 100 mL of water. Once again, they predicted the combined weight before placing the flask back on the scale and stretching the opening of the balloon over the top of the flask. They manipulated the balloons to drop the pieces of Alka-Seltzer into the water without removing the balloon. The addition of the balloons made this a closed system. They observed the scale, recording the actual combined weight of the tablet, balloon, and flask of water. Finally, they pondered the questions: What happens to Alka-Seltzer when it is placed in water? Was this a chemical change? How do you know? Which of your two predicted weights were closer to the actual weights? How do you respond to a charge that the data in the open experiment shows that matter can be destroyed?
« My favorite part had to be the Alka-Seltzer being able to inflate the balloon, » said Stella Scanlon ’29. « I found it surprising between the different masses when the Alka-Seltzer was in an open space versus a closed one. The lab was really fun and helpful to see an in-person example of the law of conservation of mass. »
« The students did a fantastic job figuring out where the mass of the Alka-Seltzer tablet went, » said Middle School Science Teacher William Bander. « As soon as they repeated the same experiment, but with a balloon to trap the gas, they were able to see the mass of the reaction remain constant. »
After the burning and fizzing experiments, it was time to return to the iron nail that had been sitting in copper sulfate all this time. The nail looked completely different where it had been exposed to the solution! They determined whether a chemical reaction occurred, and they compared their nail to their teacher’s rusty nail, determining what substance was on their nails, where that substance came from, and whether they had created matter. The student-scientists deduced that the nail did indeed go through a chemical change. By comparing it to their teacher’s rusty nail, they saw that the shiny new material on their iron nail was not rust but was a layer of copper. The copper was not magically created but came from the blue copper sulfate solution. The iron and copper had switched places, making a copper nail and an iron sulfate solution. Finally, students were challenged to show the change by noting the symbols for the reactants and the symbols for the products.
Kayra Metan ’29 said, « My favorite part of this lab was seeing how the silver nail changed when it was submerged in a blue liquid and finding out why. »
This hands-on lab resulted in a lot of learning, laughter, and collaboration for our students. « My favorite part of this lab is students using not just their eyes, but their sense of smell to deduce where the mass of the wood went, » said Bander. « It’s pretty hard to miss when you have a classroom that ends up smelling like a campfire. »
Thanks to our intrepid Eighth-Grade Science Teachers William Bander and Dr. Kris Sontheimer ’03 for safely guiding our young scientists through their experiments that allowed them to explore the Laws of Conservation of Matter and Mass through first-hand experience.